INES Mapper 165

Here are Disch's original notes:
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= Mapper 165 =
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Example Games:
--------------------------
Fire Emblem (Unl) (some weird ?Chinese? pirate version)
Notes:
---------------------------
This mapper is a strange MMC2+MMC3 hybrid. Register style, PRG, mirroring, ?and even IRQs? of MMC3, with the
CHR swapping and CHR latch functionality of MMC2.
There is 4k CHR-RAM in addition to any CHR-ROM present.
For details on MMC3, see mapper 004. For details on MMC2, see mapper 009. Both will be referenced heavily
in this doc.
Operation:
---------------------------
Register layout, PRG Setup, SRAM enabling, Mirroring, all function as they do on your vanilla MMC3.
The CHR Regs (R:0 - R:5) are used in MMC2 style:
CHR Setup:
$0000 $0400 $0800 $0C00 $1000 $1400 $1800 $1C00
+-------------------------------+-------------------------------+
| <<R:0>> or <<R:1>> | <<R:2>> or <<R:4>> |
+-------------------------------+-------------------------------+
The same latches that exist on MMC2 exist on this mapper as well, and determine the appropriate reg.
CHR page 0 is CHR-RAM, other pages are CHR-ROM.
Notes:
---------------------------
This game specifically will read ppu$xFD0 or ppu$xFE0 via $2007 to manually toggle the latch (specifically,
to swap in the CHR-RAM page). Failure to emulate this method of MMC2 latch toggling will result in garbled
graphics.